Sylvia resided with her father in the building he set up as a refuge and assisted in its upkeep and the sermons of combined religions from across the world, depending on the drifters and people grieving from loss who came across them and decided to stay. Little else is revealed, not even her last name, other than her mother, Joe's wife, was struck with cancer and eventually died. Sylvia secretly harbored a resentful hatred against her father for what she believe was paying more attention to the shelter then their family, believing her mother died neglected. With this hatred, coupled with Christian zeal, she decided to take her revenge on her father by causing a panic of violence at the religious sanctuary.
After having killed Brother Rudy, leaving his corpse tied to a bed with "LUST" painted over it, she goes after Conner Todd, a friend of hers from when they were kids, whom she was horrified to find out was gay. She dons a dollar store mask and calls his name in a man's voice, which he falls for, especially when he finds a teddy bear on the ground and gets distracted. She then chokes him with a noose, drags him off, and cuts off his fingers before force-feeding him them and carving "LIAR" in his stomach. She later does this with another resident, Valerie, who stole money from the shelter the night she was allegedly killed. In reality, she abducted Valerie with the same ruse and costume, holding her captive in a nearby shed and torturing her by having a machine slowly cut off her left hand's fingers on a repeating timer.
Sylvia's first seen with Castiel and Jack Kline, having them fill out a form, and later when she tries to reach her father when meeting with Castiel alone and then telling Jack to pass out resources to the homeless. When he asks her about Conner, she begins to cry, relaying how they used to be friends, withholding the fact that he was gay and leaving them to find out later. When Jack tells her about his mother's death and how he feels like he let his father win, she reveals how her mother died from cancer and says he should believe in God, not people. She then decides to up the ante by rigging the monitor in the shelter to screen a projection of Valerie losing anther one of her fingers, cutting it off with the message "you won't save her".
After Brother Rudy's body is found and Castiel and Jack deduce the killer's human, she's later seen outside with a friend of hers, a young black girl, who tells Sylvia she took pictures of Rudy's body and posted it all over the internet, with a lot of response. Sylvia then takes out a butcher knife and stabs her friend, accusing her of being a "non-believer", revealing herself as the killer.
Eventually, she runs off and goes back to the shed, which her father finds, leading her to hold the knife to his throat. She chastizes him for not caring enough about her mother, no matter how much he begs her to stop. When Castiel and Jack arrive, she throws Joe down and stabs Jack, who quickly heals due to being a Nephilim, to her shock. Castiel then knocks her out and restores Valerie's fingers with his powers. Sylvia is later seen being arrested while holding a rosary, shockingly by the Crossroad Demon, Zack.